Method and apparatus for translucent file system

Abstract

In a computer system having a hierarchical file structure, a file system is provided which permits users of the system to share a file hierarchy and also have a private hierarchy in which files are automatically copied to as they are modified. Through the system of the present invention, a directory appears to the user as a single directory but may actually comprise files originating from a number of directories which are connected to one another through search links. Each directory has a search link associated with it which contains the path name of the back layer or directory behind it. The first layer seen through the system of the present invention is the front layer, private to the user. The back layers behind the front layer and connected to the front layer through the search links are shared layers accessible to multiple users. Thus transparent to the user of the directory accessible comprises multiple layers comprising shared and private files. The system further provides a copy-on-write feature which protects the integrity of the shared files by automatically copying a shared file into the users private layer when the user attempts to modify a shared file in a back layer.

We claim: 
     
       1. In a multi-user computer system comprising a central processing unit (CPU), an input/output unit and memory, said CPU being controlled by an operating system, said operating system comprising a file system module, wherein the file system module organizes and controls access to files located on disks in the computer system, said file system module organizing files into file systems comprising directories said directories containing files organized in a hierarchical file structure, a method for translucently providing to a user both shared and private access to current revisions of files, said method comprising the steps of: structuring a designated file hierarchy into two or more layers whereby each layer contains at least one directory;   creating an ordered set of layers which can be shared by any number of users, wherein two or more layers of the designated file hierarchy are arranged in time-of-creation sequence such that a layer containing a less recent revision of a file in the designated file hierarchy is placed below a layer with a more recent revision of the same file;   providing one or more front layers, each containing at least one directory, with each of the one or more front layers being controlled by a particular user of the system and is not being shared with other users of the system, with files located in each of said one or more front layers being designated such that only the particular user can read from and write to the files in said particular user's front layer, and each front layer being positioned in front of the ordered set of shared layers of the designated file hierarchy;   displaying to a particular user, most recent revisions of files regardless of whether these files reside in the directory of the particular user's front layer or in the directories of the ordered set of shared layers, as if all of the files resided in the particular user's front directory.   
     
     
       2. The method of claim 1 wherein the step of creating an ordered set of shared layers further comprises a first connecting step for connecting a particular layer in the ordered set of shared layers to a layer below said particular layer by means of search links, and wherein the step for providing one or more front layers further comprises a second connecting step for connecting each of the one or more front layers to a topmost layer of the ordered set of shared layers using search links, wherein the search links are associated with a directory of each layer and comprise a path name of a directory of a layer behind the layer the search link is located in, said path name identifying the location of a directory in a file system. 
     
     
       3. The method of claim 1 further comprising steps for automatically copying a designated file from a layer of the ordered set of shared layers, into a particular user's front layer when the particular user attempts to execute a write command to the designated file, whereby the copy of the designated file in the particular user's front layer can be modified according to the write command which triggered the copy operation without the copy operation or the location of the modified copy of the designated file being evident to the particular user. 
     
     
       4. The method of claim 2 wherein the step of connecting the one or more front layers and the ordered set of shared layers through search links comprises an additional step of establishing such search links when a new layer is created. 
     
     
       5. In a multi-user computer system comprising a central processing unit (CPU), an input/output unit and memory, said CPU being controlled by an operating system, said operating system comprising a file system module, wherein the file system module organizes and controls access to files located on disks in the computer system, said file system module organizing files into file systems comprising directories and files organized in a hierarchical file structure, said directories containing the files, a translucent file system module which cooperates with the file system module, said translucent file system module comprising: organizing means for structuring a designated file hierarchy into two or more layers whereby each layer contains at least one directory;   ordering means for creating an ordered set of layers which can be shared by any number of users, wherein the two or more layers of the designated file hierarchy are arranged in time-of-creation sequence such that a layer containing a less recent revision of a file in the designated file hierarchy is placed below a layer with a more recent revision of the same file;   a first layering means for providing one or more front layers, each containing at least one directory, with each of the one or more front layers being controlled by a particular user of the system and not being shared with other users of the system, with files located in each of said one or more front layers being designated such that only the particular user can read from and write to the files in the particular user's front layer and each particular user's front layer being positioned in front of the ordered set of shared layers of the designated file hierarchy; and   display means for displaying to a particular user, most recent revisions of files regardless of whether these files reside in the directory of the particular user's front layer or in the directories of the ordered set of shared layers, as if all of the files resided in the particular user's front directory.   
     
     
       6. The translucent file system module of claim 5 wherein the ordering means for creating an ordered set of shared layers further comprises a connecting means for connecting a particular layer in the ordered set of shared layers to a layer below said particular layer by means of search links, and for connecting each of the one or more front layers to a topmost layer of the ordered set of shared layers using search links, wherein the search links are located in a directory of each layer, and comprise a path name of a directory of a layer behind the layer the search link file is located in, said path name identifying a location of a directory in the translucent file system. 
     
     
       7. The translucent file system module of claim 5 further comprising copying means for automatically copying a designated file from a layer of the ordered set of shared layers, into a particular user's front layer when the particular user attempts to execute a write command to the designated file, whereby the copy of the designated file in the particular user's front layer can be modified according to the write command which triggered the copy operation without the copy operation or the location of the modified copy of the designated file being evident to the particular user. 
     
     
       8. The translucent file system module of claim 6 wherein the means for connecting each of the one or more front layers and the ordered set of shared layers through search links comprises a means establishing such search links when a new layer is created. 
     
     
       9. The translucent file system module of claim 5 further comprising routing means to direct any file system commands from the file system module with respect to the designated file hierarchy to the translucent file system module such that the commands are executed through the translucent file system module. 
     
     
       10. The translucent file system module of claim 5 further comprising designating means for identifying directories according to a type of variant of files contained in the directories; and accessing means for accessing files located in the at least one directory of the one or more front layers and in the ordered set of shared layers, comprising identification means for identifying the type of variant of files to be accessed, wherein the particular user is provided access through the particular user's front layer directory to files located in directories identified by a variant type requested by the particular user.   
     
     
       11. The translucent file system module of claim 10 wherein a search link file is located in the at least one directory of each layer, said search link file comprising a variant type name which identifies a variant type of files contained in a directory located in a next lower layer and a path name identifying a location of a directory located in a next lower layer which contains files of a desired variant type. 
     
     
       12. The translucent file system module of claim 11 wherein the accessing means for accessing the particular user's front layer and the ordered set of shared layers further comprises means directing any file system commands from the file system module with respect to the designated file hierarchy to the translucent file system module such that the commands are executed through the translucent file system module. 
     
     
       13. The translucent file system module of claim 12 wherein each of the one or more front layers comprise at least a first and a second sub-layer, the first sub-layer comprising a directory containing those files which are not identified by a variant type and the second sub-layer comprising a directory containing those files identified by a variant type. 
     
     
       14. The translucent file system module of claim 13 further comprising copying means for automatically copying a selected file located in a layer of the ordered set of shared layers into a particular user's front layer when the particular user attempts to write the selected file, and for copying selected files which are not identified by a variant type into a directory of the sub-layer which is not identified by a variant type and for copying files which are identified by a variant type into a directory of the sub-layer identified by the variant type. 
     
     
       15. The translucent file system module of claim 5 wherein the file system module is distributed among a plurality of computer systems connected together via a computer network such that different portions of the file system are located on different computer systems connected together via the computer network. 
     
     
       16. The translucent file system module of claim 5 further comprising masking means to eliminate access to an unwanted file located in a layer of the ordered set of shared layers without deleting the unwanted file such that the unwanted file may be accessed by others sharing the ordered set of shared layers, said masking means comprising: marking means for establishing a white-out file in a particular user's front layer identifying unwanted files in a layer of the ordered set of shared layers to which access by the particular user will no longer be permitted from the particular user's front layer; and   reading means for reading the white-out file and masking out any unwanted file listed in the white-out file when any operation is performed involving the file system such that a masked unwanted file is invisible to the particular user of the system when viewed from the layer containing the white-out file or from any layer above a layer containing the white-out file.